WO1996019836A1

WO1996019836A1 - Piezoelectrically actuated driving or adjusting element

Info

Publication number: WO1996019836A1
Application number: PCT/EP1995/004991
Authority: WO
Inventors: Martin Reuter; Konrad Voigt
Original assignee: Marco Systemanalyse Und Entwicklung Gmbh
Priority date: 1994-12-21
Filing date: 1995-12-16
Publication date: 1996-06-27
Also published as: DE59505331D1; ATE177561T1; EP0799502B1; JPH10511503A; DE4445642A1; EP0799502A1; US5900691A

Abstract

A piezoelectrically actuated driving or adjusting element can be used to transmit both pure translation movements and rotation movements. The object of the invention is to develop a piezoelectrically actuated driving or adjusting element having a simple, compact and robust mechanical structure, capable of ensuring long adjustment paths and suitable for the most varied adjustment and drive tasks with in principle the same structure. For that purpose, two parallel stacks (1, 2) of piezoelectric elements are arranged as close as possible to each other. The stacks are supported at their first front surface (11, 21) on a crossbar (3,; 30) by a tilting point (111, 211). The second front surfaces (110, 210) opposite to said first front surfaces (11, 21) lie flat on a stiff common traverse (4) that rigidly interconnects both stacks. Means (5; 6) are provided to apply a symmetrical, predefinable force on the stacks (1, 2), between the crossbar (3; 30) and the traverse (4). Hinged means (6) allow opposite groups of components to be deflected, tilted and/or lifted in relation to each other when temporally offset and variable electric voltages are applied to the piezoelectric stacks.

Description

Piezo actuator drive or adjustment element

description

The invention relates to a piezo actuator drive or adjusting element according to the preamble of the first claim, which can be used both for the transmission of pure translational and rotational movements.

Piezoelectric drive and adjustment elements are already known. As the simplest design, a piezoelectric element can be supported on a stationary support on the one hand and press against an adjustable component on the other hand. When an electrical voltage is applied to the piezoelectric element, the latter expands, as a result of which the adjustable component can be deflected. In the case of structures of this type which are known in many designs, the relatively small change in length of a piezoelectric component, which is also not greater than approximately 20-30 μm in the case of stacks composed of individual elements with stack heights of the order of 20 mm maximum permitted excitation voltage is translated accordingly by lever constructions. Such an arrangement is widely used as a precision drive, for example for adjustment work (cf. company catalog from Physik Instruments, Waldbronn [1994]). The disadvantage of such arrangements, especially when installed in devices, is that, on the one hand, the piezoelectric element always has to work against the lever assemblies and corresponding restoring means, and on the other hand, that fluctuating force and temperature influences change the length of the element itself cause. In particular, different coefficients of thermal expansion of the piezoelectric material and the material of the rest of the device, for example steel, have a disadvantageous effect. To compensate for this effect, the control element must either be readjusted in the event of temperature changes, or else automatically by means of a sensitive position measuring system at the expense of the available adjustment range can be adjusted. However, these measures require considerable additional effort. Furthermore, the designs mentioned have a low inherent rigidity due to the resetting means, so that they can work quasi-statically only with short reaction times.

Furthermore, designs with piezoelectric elements are known which achieve large adjustment ranges by adding individual steps (cf. Müller, F. "Development of a piezoelectric impulse drive with pronounced clamping", Univ. Diss., Dresden [1986]; Röscher, HJ "For the optimal design of independent piezoelectric actuators with magnetic clamping for micropositioning devices", TH Diss. Karl-Marx-Stadt [1980]). In the so-called "inch worm", at least three independently operating piezoelectric stack elements are combined to form a subassembly, which contract or expand differently depending on the electrical control, as a result of which the subassembly executes movements or transmits them to the element to be driven. In addition to the rather difficult construction of such designs, these have further disadvantages. The achievable individual step sizes are relatively small and are only around 20 μm. These devices are also not self-compensated for temperature fluctuations. With them, quite high clamping forces can be achieved, which, however, in turn lead to a relatively high degree of wear during use. Another known basic variant for drive assemblies with piezoelectric components are so-called shock drives, which are designed as bending elements consisting of two piezoelectric plates which are acted upon in opposite directions by alternating electrical voltages. The points of engagement of these elements perform elliptical movements which act on a drive element and can, for example, set it in rotation. In particular, when using several such elements, astonishing rotational speeds can be achieved, but only low torques or forces can be transmitted. In addition to the low resonance frequencies, these elements also show high wear. EP 0 574 945 A1 describes a device for actuating a valve element, in which the above-mentioned problem of self-compensation in the event of temperature fluctuations is countered by the use of two piezoelectric stacks, each of which acts individually on an actuating lever for a valve. With this arrangement, tilting and / or lifting movements are generated on both legs that grip the stack and to which the stack is connected via articulation points. The piezoelectric stack elements perform essentially free movements during operation of the device, with rotary and tilting movements being superimposed. This structure is not very rigid against external forces and requires additional stops.

The invention is based on the object of specifying a piezoactuator drive or adjustment element which has a simple, compact and very rigid structure, high adjustment paths and reaction speeds, for a wide variety of adjustment and drive tasks, with basically the same structure, can be used without having the disadvantages of the prior art.

The object of the invention is achieved by the characterizing features of the claims. The essence of the invention is that two stacks of piezoelectric, in particular piezoceramic, material are subjected to a symmetrically acting force in a holder, are clamped in such a way that they experience defined changes in length when an electrical voltage is applied, the symmetrically acting prestressing force being retained , and said change in length can be transferred to the overall device or suitable drive means with a high transmission ratio or high force.

The invention will be explained in more detail below with reference to ten exemplary embodiments and the attached schematic drawings. Show it.

1 shows a schematic structure of a pure translation element designed according to the invention, 2 shows a schematic structure of a drive element designed according to the invention, with which drives, in particular stepper drives, are also made possible,

3 shows a further schematic structure which is within the scope of the invention,

4 shows a schematic structure according to the invention, in which a symmetrical biasing force is applied by asymmetrically arranged means,

4a shows a mirror-symmetrical arrangement of two assemblies according to FIG. 4,

5 shows a construction according to the invention in a schematic plan view, in which four piezoelectric stacks are used,

6 shows a schematic structure in which an adjustment in several coordinate directions is made possible using elements according to the invention,

Fig. 7 shows a variant of a linear structure of a drive with two elements according to the invention

Fig. 8 is a schematic plan view of an arrangement according to the invention for shifting or rotating a

Table,

9 and 10 schematically illustrated arrangements for the rotary drive of shafts or hollow cylinders using drive elements according to the invention.

In FIG. 1, a component according to the invention, which is to be referred to in its entirety hereinafter as 10, is shown in the rest position, in which two piezoceramic assemblies 1, 2, which are in stack form, are arranged parallel to one another at a distance of 1 mm - are arranged. End faces 11 and 21 of each stack are supported on a leg 3 on the one hand via a tiltable connection 1 1 1 or 211, which in the example can be designed as a solid body articulated in one dimension. On the other hand, the second stack end faces 110 and 210 are jointly gripped by a rigid crossmember 4, on which said second end faces rest flat and rigid. In the example, the traverse 4 has a center arranged between the stacking axes fixed body joint 8. The assemblies mentioned so far are clamped in a Festköφeφarallelogram, which is formed from said leg 3, another leg 7 and means 5, 6 connecting these on both sides. It is also within the scope of the invention to implement the clamping and symmetrical application of force to the two stacks 1, 2 mentioned by means of a tie rod, not shown, arranged symmetrically to the stacks 1, 2. Means 6 are designed in the example as fixed-body joints. Preloading means 5 acting parallel to the stacking axes mentioned can be supplemented, for example, with screws or the like, which have a defined one

Setting the preload, which is on the order of 20 -

25 N / mm ² should allow, which are not shown in detail, since the absolute magnitude of the biasing force the basic

Functionality of the invention is not affected. If the piezoceramic stacks are now subjected to differing electrical voltages, this leads to a contraction or expansion of the stacks which deviate from one another in their axial direction, which is indicated by arrows, which causes the stacks to tilt slightly, which in turn via the solid body joint 8 of the common traverse 4 the leg 7 are engaged and thus a lateral deflection of the Festköφeφarallelogramms (indicated by a double arrow) because of the possibility of evasion created by the Festköφer joints 6 entails. In this way, when using approximately 20 mm high piezoceramic stacks, which continue to have only length changes between 20 μm to 30 μm when the maximum voltage can be applied, lateral deflections of the fixed body parallelogram in the order of magnitude of 200-250 μm can be translated. The main advantages of the arrangements described (and also to be described below) are that

the device is self-compensated for temperature changes by using two stacks,

- When the stack is electrically charged, no work is to be done against the legs 3 and 7 or other pretensioning means, which is why the pretensioning can be designed to be very rigid in this mode of operation, large excursions with simultaneously defined and precisely adjustable absolute excursions can be achieved,

- With electrical charging of the stack in push-pull, a defined active resetting (or counter-deflection in another direction) of the device takes place and without an additional external force

- Extremely short positioning times (approx. 1 ms) can be achieved without overshoot or resonance.

Another structure 10 'within the scope of the invention is shown schematically in FIG. Basically analogous to FIG. 1, here again two piezoceramic stacks 1, 2 are clamped between one leg 3 and a common rigid cross-member 4. In the example, the crossbeam 4 is given a spherical surface without restricting its other further design within the scope of the respective use. In contrast to FIG. 1, the symmetrical application of force to the two stacks is realized by spring means symmetrically surrounding the stack, which in the example are designed as spiral springs 5, which not only have a force due to their connection to the cross member 4 and the leg 3 exert on the stack, but at the same time also take on the function of the solid joints 6 (as in FIG. 1). An electrical voltage control analogous to FIG. 1 is also possible here. However, electrical control of the two stacks 1, 2 with a selectable phase shift of a sine voltage component, for example at 90 °, is of particular importance. In this case, the movement which the culmination point 9 of the traverse 4 carries out becomes more complicated; it then executes an elliptical movement which is indicated by dashed lines. In the direction of the small semiaxis z, an untranslated change in length of the stacks 1, 2 acts in the same direction. The stroke in this direction is small, but large forces can be transmitted. The size of the stroke in the z direction is influenced by the spring characteristic of the biasing springs 5. The lower their stiffness, the greater the stroke that can be achieved in this direction and only limited by the maximum achievable expansion of the stacks 1, 2. Such an embodiment and mode of operation of the invention is particularly suitable for its use as a stepper drive. If you leave the traverse 4 in the phase one Press expansion in the same direction in the x direction against a translationally movable counter surface 90, so that a force-locking connection is established, so in the subsequent phase this counter surface is displaced in the x direction with lever-translated deflection. In the contraction phase of the stack, the connection mentioned comes loose and there is a free backward movement of the crossmember until a non-positive connection is established again. When using piezoelectric stacks with typical lengths of 20 mm, a stroke of approx. 15 μm in the z direction and a deflection of approx. 200 μm in the x direction can be achieved. If the expansion of the stacks 1, 2 in the clamping direction is limited when the coupling surface is reached, the stack has a high clamping force because of the high inherent rigidity. If the traverse 4, as shown in the example, is formed with a rounded surface, or is additionally provided with such a surface, then a linear coupling to the counter surface to be driven can take place, which requires little adjustment effort, which ensures particularly low-wear operation. Such a drive can easily be operated at 1 kHz, which means that feed speeds of at least 100 mm / s can be achieved. By adjusting the phase angle between 0 ° and 180 °, the movement amplitude and thus the step size from 0 - 200 μm can be set continuously and the function of a continuously operating transmission can be realized. Phase angles between 180 ° and 360 ° generate corresponding steps in the opposite direction. For fine positioning, the actuating operation can be implemented with the highest precision by statically actuating the stack in push-pull according to the exemplary embodiment in FIG. 1.

A further embodiment of the invention is shown in FIG. This arrangement produces a stroke (Δz) in the z direction at φ = 0 ° and a tilt (Δαr) of the leg 3 about a point 9 'at φ = 180 °, which is achieved by attaching a lever 12 shown in broken lines into a translation (Δx ) can be converted in the x direction. The advantage of such a design is a translation in the x-direction that can be adjusted by the length of the lever 12 and the low mass that can be effectively moved, as a result of which even greater reaction speeds than 1 and FIG. 2 are achievable. Likewise, said lever 12 can also be angled if no stroke is required.

FIG. 4 shows another possible embodiment according to the invention, in which the required symmetrical application of the pretensioning force to both piezoelectric stacks 1, 2 is carried out by means of asymmetrically attached push and pull elements 5 ', 5 " A laterally arranged push rod 5 'enables the lateral deflection of the arrangement mentioned under Fig. 1. Drive bodies which are to be designed accordingly and are not shown in more detail can, for example, be additionally attached to a cross rod 91. An embodiment according to this figure permits a particularly space-saving and mass-saving structure of the Force generation and tilting elements as well as the traverse 4 and thus very high reaction speeds, because of the possibility created with such an embodiment, the formation of a mirror-symmetrical arrangement with very closely adjacent coupling points, as shown schematically in FIG he respective stack pairings are indicated in push-pull), an extremely quiet operation of the overall device is guaranteed.

FIG. 5 schematically shows a partial arrangement in plan view, in which not only two piezoelectric stacks are used, as previously described, but four, which, as in FIGS. 1 and 2, are not attached to one leg 3 but to one Press on leg plate 30. The piezoelectric stacks 1, 1 ', 2, 2' are arranged distributed in the square. Depending on whether this arrangement is held on a traverse plate 40 or the leg plate 30, a two-dimensional xy shift or a two-dimensional tilting about the x and y axis results, analogously to FIGS. can be converted into an xy shift by a lever (not shown here) (analogous to lever 12 in FIG. 3). By means of a control described in accordance with the second and third exemplary embodiments, these forms of movement can each be combined with stroke movements in the z direction (ellipses). Such a 4-stack arrangement is extremely compact and can be adjusted by an xy Replace the drive, consisting of two orthogonally connected, one-dimensional arrangements, as explained below. However, the possibility of tilting the single-stack connection on the side of the side plates must be such that more than one degree of freedom is permitted. This can be achieved, for example, by means of a cone-shaped, preferably mushroom-shaped, in particular as a solid body coupling points.

FIG. 6 shows, in a very simplified form, a combination of two elements 10 according to the invention, which are firmly connected on one side in such a way that their directions of action are orthogonal to one another and also connected, as a result of which an x-y adjustment drive of a table 92 indicated by dashed lines can also be realized. Compared to an embodiment according to FIG. 5, this construction according to the invention is somewhat more voluminous, but more manageable in the electrical wiring of the piezoelectric stacks. As can be easily recognized, an x-y-z adjustment drive can be manufactured in a simple manner by a further connection of a third element 10 according to the invention with the direction of action shown to be again orthogonal.

FIG. 7 shows a further possibility of a step drive with several elements according to the invention. The two drive elements 10 according to the invention are opposite each other by 180 °, but are otherwise arranged in one plane. If both are subjected to identical voltage profiles symmetrically, they both also act simultaneously on an element 93 to be driven, the coupling forces acting on the element 93 mutually compensating one another, which leads to the following advantages:

- precise coupling and uncoupling with a small stroke, - no excitation of resonances of the element 93 and

- Little effort for storage and management.

Likewise, in this embodiment, instead of the schematically indicated drive elements 10, a drive design according to FIG. 4a can be used, in which case the drives formed by 10'a and 10T) and arranged on a common basis (see FIG. 4a) in FIG Be operated push-pull. This causes one of the drive pairs, 7, always remains in push-pull with respect to the element to be driven in the coupled position, while the other is in the return movement. The base is loaded much more evenly and only tilting forces occur that can be compensated for by a parallelogram connection to a housing.

FIG. 8 schematically shows a top view of individual drives 10 arranged parallel to one pair and the pairs orthogonally to one another. On the one hand, these individual drives 10 can be driven in pairs in the same direction, with the voltage profiles mentioned, so that a successive or parallel x-y displacement of an adjustment table 92 shown in broken lines is possible. On the other hand, it is also possible to control opposing individual elements in pairs in the opposite direction, whereby the table 92 can be set in rotation. The directions of movement that can be achieved are indicated by double arrows.

FIGS. 9 and 10 describe design forms in which a plurality of drive elements 10 ′ according to the invention act either on the outer circumference of a shaft 94 (FIG. 9) or on the inner circumference of a hollow cylinder 95 (FIG. 10). A step drive for rotating movements can also be implemented in this way. The number of elements 10 according to the invention which are used in this case and thus the maximum achievable clamping force can be easily adapted in accordance with the torque to be applied. Likewise, the electrical control of all drive elements 10 can be selected as desired with respect to their step size and the time sequence with respect to one another, e.g. to achieve optimal concentricity.

In all the drive tasks described, it should be noted that for a given type of attachment of a pair of stacks, the adjustment path that can be achieved depends on the magnitude of the counterforce. If the counterforce exceeds the so-called blocking force, the travel path becomes zero. Likewise, a piezo actuator according to the invention can reach its maximum Hubs no longer generate force; However, well-made piezo stacks have a very high inherent stiffness and at least 20 mm, with a cross section of 8 x 8 mm, have blocking forces in the order of magnitude of 2 kN. For each actuator type, the stroke that can actually be carried out at a given excitation voltage depends on the special conditions of use.

All features shown in the description, the following claims and the drawing can be essential to the invention both individually and in any combination with one another.

1, 2 stacked piezoelectric elements

10, 10 ',

10'a, 10'b - overall elements according to the invention

11, 21 first stack ends

110, 210 - second stack ends

111, 21 1 tiltable connections, 7 legs

Traverse 0 Traverse plate, 5 ', 5 "- means for applying force to articulated means

Fixed body joint

Culmination point 'tilt point

12 lever 0 counter surface 1 cross bar 2 table 3 element to be driven 4 shaft 5 hollow cylinder

Claims

claims

1. Piezo actuator drive or adjusting element, which contains at least two piezoelectric assemblies (1, 2) in stack form, characterized in that a) said stacks (1, 2) are arranged as closely as possible in parallel, b) the stacks each on the one hand with its first stack end face (11, 21) via a tiltable connection (111, 211) on one leg

(3; 30) are supported and c) the aforementioned first stack end faces (1 1, 21) respectively opposite second stack end faces (110, 210) are rigidly connected to one another by means of a rigid cross beam (4) on which said second stack end faces lie flat d) means (5; 6) are provided, apply a symmetrically acting, predeterminable force to the said stack (1, 2) between the leg (3; 30) and the crossmember (4) and e) articulated means (6) are provided which

- either a relative deflection and / or a stroke of the cross member (4; or component 7) opposite the leg (3; 30) held in the rest position

- Or a relative tilting and / or a stroke of the leg opposite the crossbar (4) held in the rest position

(3; 30) when applying temporally and mutually variable electrical voltages to said piezoelectric stack.

2. Piezo actuator drive or adjusting element according to claim 1, characterized in that said articulation means in the form of fixed body joints (6; 111, 211) are formed within, on said two piezoelectric stacks (1, 2) symmetrically acting assemblies .

3. Piezo actuator drive or adjusting element according to claim 1, characterized in that said articulation means in the form of fixed body joints (6) within at least one, said two piezoelectric stack asymmetrically detecting pressure element (5 ^* ), such as a push rod, formed are.

4. Piezo actuator drive or adjusting element according to claim 1, characterized in that said articulation means and means for applying force in the form of spring elements (5; 6) arranged symmetrically to said two piezoelectric stacks, such as e.g. Bending springs are formed.

5. Piezo actuator drive or adjusting element according to claim 1, 2 or 3, characterized in that said articulation means are arranged via an essentially centrally acting and symmetrical to said second stack end faces (110, 210), preferably designed as a fixed-body joint ( 8) mentioned traverse (4) are detected.

6. Piezo actuator drive or adjusting element according to claim 1, characterized in that a symmetrical application of force to said two piezoelectric stacks (1, 2) takes place over a comprehensive These these Festköφeφarallelogramm (7, 6, 5, 3).

7. Piezo actuator drive or adjusting element according to claim 1, characterized in that a symmetrical application of force to said two piezoelectric stacks (1, 2) takes place via a tie rod arranged symmetrically to said stacks.

8. Piezo actuator drive or adjusting element according to claim 1 and 3, characterized in that a symmetrical Kraftbe¬ application of two piezoelectric stacks (1, 2) via this asymmetrically detecting pressure and tension elements (5 ', 5 ").

9. Piezo actuator drive or adjusting element according to claim 1, characterized in that said piezoelectric stack (1, 2) can be acted upon with temporally variable in their difference and / or their mean value electrical voltages.

10. Piezo actuator drive or adjusting element according to claim 9, characterized in that said stack can be acted upon in addition to an elec¬ tric DC bias with an AC voltage, a phase shift of said AC voltage between the stacks (1, 2) between 0 ° φ ≤

360 °, depending on the application of the drive element, can be variably preset and set.

1 1. Piezo actuator drive or adjusting element according to claim 9 or 10, characterized in that an average of said

Stacking (1, 2) of the applied DC bias is kept constant and only a differential voltage component is subjected to variation.

12. Piezo actuator drive or adjusting element according to one of claims 1 to 8 and 9 to 1 1, characterized in that four piezoelectric stacks (1, 1 ', 2, 2') like a carriage between a common plate-shaped leg plate (30) and a crossbar plate (40) are attached, wherein in pairs, adjacent to each other, piezoelectric stacks, depending on the desired direction of action, can be acted upon with identical electrical voltages or voltage profiles.

13. Piezo actuator drive or adjusting element according to claim 12, characterized in that said tiltable connection of each individual piezoelectric stack to said leg plate via conical, preferably mushroom-like, in particular as

Fixed body trained coupling points takes place. 14. Piezo actuator drive or adjustment element according to one of the preceding claims, characterized in that a plurality of said complete drive or adjustment elements are combined to form a common drive or adjustment unit.

15. Piezo actuator drive or adjusting element according to claim 14, characterized in that at least two elements, consisting of two named piezoelectric individual stacks, are used in a linear arrangement, the stack pairs being symmetrical, in particular in common mode, with identical ones Voltages or voltage profiles can be applied.

16. Piezo actuator drive or adjusting element according to claim 14, characterized in that at least two elements, consisting of two named piezoelectric individual stacks, are used in a linear arrangement, the stack pairs being asymmetrical, in particular push-pull, with identical ones Voltages or voltage profiles can be applied.

17. Piezo actuator drive or adjusting element according to claim

14, characterized in that at least two elements, each consisting of two named piezoelectric individual stacks, are used in an orthogonal arrangement with respect to their direction of action, with all stack normals running parallel in the rest position.

18. Piezo actuator drive or adjusting element according to claim 14, characterized in that at least two elements, consisting of two named piezoelectric individual stacks, are used with respect to their direction of action in an orthogonal arrangement, the stack standards of the respective individual elements being at rest - Position perpendicular to each other. 19. Piezo actuator drive or adjusting element according to claim 18, characterized in that said two individual elements are in one dimension in a fixed connection.

20. Piezo actuator drive or adjusting element according to claim

14, characterized in that a plurality of said stack pairs are arranged in a rotationally symmetrical manner to a drive element and alternately act on said drive element by applying appropriate voltage.